Abstract
A non-thermal plasma-water system using a microsecond pulsed high-voltage power supply was investigated with air, nitrogen, oxygen, and argon gas feedings individually. Optical emission spectroscopy (OES) was utilized to characterize the primary active species inside the plasmas generated by different gas feedings. The OES method was also employed to estimate the neutral gas and electron temperatures. The pH and the oxidation-reduction potential (ORP) of plasma-activated water (PAW) were measured in the liquid phase. An ion chromatography system (ICS) was employed to present the PAW activity, such as nitrite and nitrate species. Moreover, hydrogen peroxide as a secondary active species inside the activated water, generated by the gases mentioned above, was measured by potassium permanganate titration. It was found that the gas species have a noticeable effect on the pH level as well as the ORP of PAW. In the cases of argon and oxygen plasmas, the pH level of PAW does not change significantly. In contrast, the pH values of PAW generated by air and nitrogen plasmas decline sharply during the treatment time. Moreover, the gas species have a significant impact on the concentrations of nitrite, nitrate, and hydrogen peroxide generated in PAW. The activated water generated by oxygen plasma provides the highest level of hydrogen peroxide. Although the consumed power of argon plasmas was half of the other plasma sources, it provides relatively high hydrogen peroxide contents compared to the nitrogen and air plasmas.
Highlights
In an interaction between non-thermal atmospheric pressure plasma (NTAPP) and water, a process appears, such as plasma-activated water (PAW), that provides wide applications [1,2]
The effect of gas species was investigated by various dielectric barrier discharge (DBD) plasmas with air, nitrogen, oxygen, and argon gas feedings on PAW properties
It was found that the air and nitrogen plasmas provide an acidic medium, whereas, in the cases of oxygen and argon, the pH does not change significantly
Summary
In an interaction between non-thermal atmospheric pressure plasma (NTAPP) and water, a process appears, such as plasma-activated water (PAW), that provides wide applications [1,2]. Following the generation of enormous chemically active species in the gas phase by NTAPP in the interaction with water, PAW initiates chemical reaction processes inside the water leading huge amount of chemically active species. The discharge volume and energy efficiency significantly change with water conductivity [7] that causes difficulties to ignite discharge as well as discharge instabilities inside the water. To overcome this problem, the discharge is generated in a gas phase over a water surface [8]. Dielectric barrier discharge (DBD) is developed as an NTAPP over the water surface for PAW to control and stabilize the discharge
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